Figure 1. Measuring the ligula distance from the occlusal plane on the trace of a panoramic radiography.

1: Orbital point: the lowest point of the infraorbital margin

2: The most superior point of the mandibular lingula

P₁: orbital plane: line to the orbital points

P₂: plane parallel to the orbital plane passing through the most superior point of the mandibular lingula

P₃: Occlusal plane: tangent to the tips of the cusps of the lower posterior teeth